1. Field of the Invention
The present invention relates to an apparatus and a method for measuring concentrations of components with light scattering, in which the concentrations of the components in an object are measured in non-destructive fashion by making use of Raman scattered light.
2. Description of the Prior Art
Conventionally, there has been known an apparatus for measuring concentrations of components in citrus fruits in non-destructive fashion by making use of Raman scattered light (Japanese Patent Laid-Open Publication No. 4-254744 (1992)).
This apparatus is so arranged that laser of a wavelength in visible radiation range (e.g. wavelength: 514.5 nm) is irradiated to a citrus fruit and, taste of the citrus fruit is determined, based on the intensity of Raman scattered light generated due to carotenoid contained in the pericarp of the citrus fruit. Further, the saccharic acid ratio of the citrus fruit is estimated from the content of carotenoid contained in the pericarp of the citrus fruit so as to judge the taste.
In the above conventional apparatus, laser of a wavelength in visible radiation range is used to calculate the content of carotenoid contained in the pericarp of a citrus fruit, which is the measuring object. The laser of a wavelength in visible radiation range is low in transmissivity when it is applied to the measuring object, and large in attenuation factor due to absorption and scattering in the measuring object. Therefore, it could be considered that, in the above apparatus, the content of carotenoid contained in the fruit is estimated by measuring the quantity of Raman scattered light derived not from the fruit itself but from its pericarp, i.e. its surface layer, so as to judge the taste of the citrus fruit.
Further, laser of a wavelength in visible radiation range has large quantum energy, as compared with laser in near-infrared wavelength range.
As a result, when the measuring object is a living body such as in clinical medicine tests, such a problem arises that use of the laser in a wavelength in visible radiation range that will reach a measurement site within the living body would result in destruction of structures in the living body.
Further, when the laser of a wavelength in visible radiation range is irradiated to measure concentrations of components in the measuring object, such further problems arise that Raman spectroscopy on the living body by laser excitation in the visible radiation range would involve generation of fluorescence from the living body as well as a more frequent occurrence of photolysis, i.e. photochemical reaction.
The fluorescence and photochemical reaction are likely to be produced by the following cause.
In the case of the conventional laser excitation in the visible wavelength range, the energy of a light quantum is high relative to targeted transition energy, such that electrons can be excited not only to a vibrational level that causes a targeted Raman scattered light to be generated, but also to a high energy level of different electron state. Therefore, it is considered that when Raman scattering occurs due to transition between energy levels, an excitation to high energy level also occurs, which results in fluorescence generation. As a consequence of this, a more intense background signal of Raman spectrum results, making the measurement of spectrum difficult to achieve.
It is considered that the photochemical reaction would occur due to the relatively high energy of light quantum of the laser of a wavelength in visible radiation range. Namely, it is considered that after absorption of energy of the laser by a substance, its molecular structure would vary, thus resulting in the photochemical reaction. As a result, the structure of the measuring object would be damaged as viewed microscopically, so that the analysis would no longer be a non-destructive analysis in a strict sense. In particular, when laser Raman spectroscopy is applied to analysis of living bodies or foods, the above problem would be clearer because these substances in many cases contain components that are complex and easily subject to photolysis.